Hello Paulo,

You don't need to recreate the image.py file. You can use its methods by importing it from odoo.tools:

`from odoo.tools import image_resize_images`

You should use the method image_resize_images with a specified parameter size , like is in the following example:

image_resize_images(vals, big_name='cover', medium_name='cover_medium', small_name='cover_small',
                    size={'cover': (1550, None), 'cover_medium': (1000, None), 'cover_small': (420, None)})

The Odoo way of using that technique for storing 3 types of image sizes is by defining 3 fields
 for images in your model, that represents big_image, medium_image and small_image.

Use this method by calling it in create and write methods in the model, like this:

@api.model
def create(self, vals):
    image_resize_images(vals)
    return super(PaymentAcquirer, self).create(vals)

@api.multi
def write(self, vals):
    image_resize_images(vals)
    return super(PaymentAcquirer, self).write(vals)

The example is from payment_acquirer.py in the payment module. You can see it for more information.

Regards,

Lyubo.